Electrode base, negative electrode for aqueous solution electrolysis using same, method for producing the electrode base, and method for producing the negative electrode for aqueous solution electrolysis

ABSTRACT

The negative electrode for aqueous solution electrolysis of the present invention includes a conductive substrate having a nickel surface, a mixture layer including metal nickel, a nickel oxide and carbon atoms, formed on the conductive substrate surface, and an electrode catalyst layer formed on the mixture layer surface, wherein the electrode catalyst layer is formed by a layer including a platinum group metal or a platinum group metal compound. The negative electrode for aqueous solution electrolysis of the present invention is preferably used in electrolysis of an aqueous solution of an alkali metal halide, and the like.

TECHNICAL FIELD

The present invention relates to an electrode base used in an electrodefor aqueous solution electrolysis. In addition, the present inventionrelates to a negative electrode for aqueous solution electrolysis inwhich an electrode catalyst layer is formed on the electrode base andwhich is preferably used as a negative electrode for electrolysis of anaqueous solution of an alkali metal halide, and a production methodthereof.

BACKGROUND ART

In an electrolysis industry consuming a large amount of electric power,reduction of energy required for production is getting to be a biggerissue, in terms of reduction of electric power consumption rate, andreduction of carbon dioxide emission as measures against global warming.In order to reduce energy required for electrolysis, an electrode, anion-exchange membrane and an electrolytic cell are particularly gettingadvanced.

Negative electrodes for aqueous solution electrolysis having a lowhydrogen overvoltage and a long operating life have been proposed as anegative electrode for aqueous solution electrolysis used in an aqueoussolution electrolysis, which are obtained by forming, on a base made ofnickel, an electrode catalyst layer including a platinum group metal ormetal oxide, or an electrode catalyst layer including a rare earth metalsuch as a lanthanum or its compound and a platinum group metal.

These negative electrodes for aqueous solution electrolysis have a lowhydrogen overvoltage, and a feature in which they have smoother surfacesof the electrode catalyst layer than that of conventional electrodeshaving particulate substances deposited on the surface, and thus damagecaused by repetitive contact with an ion-exchange membrane can beprevented even if the electrolysis is performed with the ion-exchangemembrane being in close contact with the electrode.

However, because the metal nickel, which is used as the base of thenegative electrode for aqueous solution electrolysis, is brought intocontact with the electrode catalyst layer showing a more noble potentialthan the nickel, the nickel base is easily corroded due to galvaniccorrosion during a downtime of electrolysis or exposure to theatmosphere.

In addition, if a electrolytic cell is assembled from negativeelectrodes, positive electrodes and ion-exchange membranes and then thecell is stored in a state in which an electrolytic solution is notfilled in the electrolytic cell, nickel ions generated by corrosion ofthe nickel base, which is caused by contact of the negative electrodewith the ion-exchange membrane, permeate into the ion-exchange membraneto cause a phenomenon that the ions are deposited in the ion-exchangemembrane as a nickel compound, which leads to deterioration ofproperties of the ion-exchange membrane and thus sometimes to a rise ofan electrolysis voltage and a decrease in current efficiency.

In order to solve such defects, a method for producing a negativeelectrode has been proposed in which a nickel substrate surface isheated and baked at a temperature of 350 to 550° C. for 5 to 60 minutesto form an intermediate layer including a nickel oxide as a maincomponent on the conductive base surface (see, for example, PatentDocument 1). The document describes that according to this method, theadhesion is strong because the intermediate layer and the base areformed from an originally integral material, and therefore peeling-offor lacking of the intermediate layer is not caused.

In addition, the present applicant has proposed a negative electrode foraqueous solution electrolysis including an electrode catalyst layercontaining a platinum group metal compound and a lanthanoid, which hassuperior electrolysis properties (see, for example, Patent Document 2).

PATENT DOCUMENT

-   Patent Document 1: Japanese Patent No. 4142191-   Patent Document 2: Japanese Patent No. 4274489

SUMMARY OF INVENTION Technical Problem

The negative electrode described in Patent Document 1 seems that elutionof the nickel component from the electrode base can be prevented.However, the document also describes that the cell voltage is risenafter the electrolysis is started and then the electrolytic celloperation is shutdown.

The electrode described in Patent Document 2 has superior electrolysisproperties to those of similar kinds of conventional electrodes, butresistance to reverse current is required to be more sufficient atemergency shutdown of the electrolytic cell operation, and the like.

Solution to Problem

The present invention aims to provide an negative electrode for aqueoussolution electrolysis whose electrode base is a conductive substratehaving nickel on its surface, which prevents elusion of nickel from theelectrode base, prevents elusion of nickel from the negative electrodebase during storage of an electrolytic cell integrally assembled fromthree components of a positive electrode, an ion-exchange membrane andthe negative electrode in the atmosphere or suspension of theelectrolytic cell operation, and is little affected by a reverse currentgenerated at the time of emergency shutdown of the electrolytic celloperation. The present invention also aims to provide a negativeelectrode for aqueous solution electrolysis, having a low electrolyticcell voltage at the start of initial operation as well as at re-start ofoperation after shutdown of the electrolytic cell.

The present invention has the following constitution features [1] to[15].

[1] An electrode base including a mixture layer including metal nickel,a nickel oxide and carbon atoms, formed on a surface of a conductivesubstrate having a nickel surface.

[2] The electrode base according to the item 1 above, wherein themixture layer is formed by applying a nickel compound including a nickelatom, a carbon atom, an oxygen atom and a hydrogen atom to the surfaceof the conductive substrate, and performing a thermal decomposition.

[3] The electrode base according to the item 2 above, wherein the nickelcompound is either of a nickel formate and a nickel acetate.

[4] A negative electrode for aqueous solution electrolysis including:

a conductive substrate having a nickel surface;a mixture layer including metal nickel, a nickel oxide and carbon atoms,formed on the surface of the conductive substrate; andan electrode catalyst layer including a platinum group metal or aplatinum group metal compound, formed on a surface of the mixture layer.

[5] The negative electrode for aqueous solution electrolysis accordingto the item 4 above, wherein the electrode catalyst layer furtherincludes a lanthanoid compound.

[6] The negative electrode for aqueous solution electrolysis accordingto the item 5 above, wherein the electrode catalyst layer is formed bythermally decomposing an electrode catalyst layer-forming solutionincluding a ruthenium nitrate and a lanthanum acetate at 400° C. to 600°C. in an atmosphere containing oxygen.

[7] The negative electrode for aqueous solution electrolysis accordingto the item 6 above, wherein the electrode catalyst layer-formingsolution further includes a platinum compound.

[8] The negative electrode for aqueous solution electrolysis accordingto the item 5 above, wherein the electrode catalyst layer includes acerium oxide and platinum.

[9] A method for producing an electrode base including the steps of:

applying a nickel compound including a nickel atom, a carbon atom, anoxygen atom and a hydrogen atom to a surface of a conductive substratehaving a nickel surface; andperforming thermal decomposition at 250° C. to 600° C. in an atmospherecontaining oxygen, thereby forming a mixture layer including metalnickel, a nickel oxide and carbon atoms.

[10] The method for producing an electrode base according to the item 9above, wherein the nickel compound is either of a nickel formate and anickel acetate.

[11] A method for producing a negative electrode for aqueous solutionelectrolysis including the steps of:

producing an electrode base by applying a nickel compound including anickel atom, a carbon atom, an oxygen atom and a hydrogen atom to asurface of a conductive substrate having a nickel surface, andperforming thermal decomposition at 250° C. to 600° C. in an atmospherecontaining oxygen, thereby forming a mixture layer including metalnickel, a nickel oxide and carbon atoms; and forming an electrodecatalyst layer by applying an electrode catalyst layer-forming solutionincluding a platinum group metal compound to a surface of the mixturelayer of the electrode base, and performing thermal decomposition in anatmosphere containing oxygen.

[12] The method for producing a negative electrode for aqueous solutionelectrolysis according to the item 11 above, wherein the nickel compoundis either of a nickel formate or a nickel acetate.

[13] The method for producing a negative electrode for aqueous solutionelectrolysis according to the item 11 or above, wherein the electrodecatalyst layer-forming solution includes a ruthenium nitrate and alanthanum acetate, and the electrode catalyst layer is formed byapplying this electrode catalyst layer-forming solution to the surfaceof the mixture layer of the electrode base and then thermallydecomposing it at 400° C. to 600° C. in an atmosphere containing oxygen.

[14] The method for producing a negative electrode for aqueous solutionelectrolysis according to the item 13 above, wherein the electrodecatalyst-forming solution further includes a platinum compound.

[15] The method for producing a negative electrode for aqueous solutionelectrolysis according to the item 11 or above, wherein the electrodecatalyst layer-forming solution further includes a cerium nitrate.

Advantageous Effects of Invention

The electrode base of the present invention is one in which a mixturelayer including metal nickel, a nickel oxide and carbon is formed on aconductive substrate having nickel on its surface by thermaldecomposition of a nickel compound composed of nickel atoms, carbonatoms, oxygen atoms and hydrogen atoms such as a nickel carboxylate at alow temperature. Due to the presence of the mixture layer, even if areverse current flows to a negative electrode in a case of, for example,emergency shutdown of electrolytic cell operation, nickel does not elutefrom the nickel substrate to deposit in an ion-exchange membrane. Inaddition, due to the presence of the mixture layer, corrosion resistanceof the conductive substrate is enhanced and also adhesion between theconductive substrate and the electrode catalyst layer is increased.Furthermore, an initial potential stability is high when electrolysis isstarted, the electrolysis can be stably operated right from thebeginning, and a negative electrode for aqueous solution electrolysishaving a small hydrogen overvoltage can be provided. In particular, theeffects described above is more extensive when the mixture layer isformed by thermal decomposition of a nickel carboxylate as typified bynickel formate or nickel acetate at a low temperature.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing results of anodic polarization tests of anegative electrode of the present invention.

FIG. 2 is a diagram showing change in a negative electrode potential inone Example of the present invention.

FIG. 3 is a diagram showing change in a negative electrode potential inanother Example of the present invention.

FIG. 4 is a diagram showing change in a negative electrode potential instill another Example of the present invention.

FIG. 5 is a diagram showing change in a negative electrode potential instill another Example of the present invention.

DESCRIPTION OF EMBODIMENTS

The electrode base of the present invention is one in which a mixturelayer including metal nickel, a nickel oxide and carbon atoms isprovided on a surface of a conductive substrate having a nickel surface.

The electrode base of the present invention has the mixture layerincluding the metal nickel, nickel oxide and carbon atoms on theconductive substrate having the nickel surface, and therefore theelectrode base has an advantage in which it is not broken even at thetime of occurrence of anodic polarization, which is caused by reversecurrent occurring when electrolytic power is urgently stopped duringelectrolytic cell operation to shut down the operation, and after theelectricity is turned on again, the operation can be performed just asthe operation was performed before it was shutdown.

In the present invention, the conductive substrate having a nickelsurface refers to nickel, or one in which a nickel layer is formed on asurface of a conductive material such as stainless steel, iron or copperby plating or cladding.

It is apparent that the mixture layer is a layer in which the metalnickel, the nickel oxide and the carbon atoms exist in a mixed state,from its analysis results. Though the reason why excellent propertiescan be obtained by providing such a mixture layer is not clear, it canbe considered that the mixture layer has a good adhesion with the nickelsurface of the conductive base, it has corrosion resistance even if itis subjected to an anodic polarization, and it suppresses a corrosionreaction with the conductive substrate surface.

The electrode base of the present invention may be produced by, forexample, a method shown below.

The nickel compound composed of nickel atoms, carbon atoms, oxygen atomsand hydrogen atoms is applied to the surface of the conductive substratehaving the nickel surface, and the resulting substrate is baked in anatmosphere containing oxygen, for example, in the atmosphere. Thus, themixture layer including the metal nickel, the nickel oxide and thecarbon atoms can be formed. The nickel compound can be applied to theconductive substrate surface by, for example, coating the surface with acoating solution including the nickel compound. Organic acid salts ofnickel can also be used as the nickel compound, and nickel carboxylatesas typified by nickel formate and nickel acetate are particularlypreferably used.

The mixture layer is preferably baked at a temperature of 250° C. to600° C., and more preferably 250° C. to 500° C.

The baking time is preferably from 5 minutes to 60 minutes, and morepreferably from 5 minutes to 30 minutes.

The thermal decomposition reaction of the nickel carboxylates such asnickel formate and nickel acetate can proceed at a lower temperaturecompared with the reaction of inorganic salts such as nickel nitrate andnickel sulfate, and the nickel surface of the base is not seeminglyaffected, because acidic gases capable of causing metal corrosion suchas nitrogen oxides and sulfur oxides are not generated upon the baking.In addition, the method has features that a special removing facility isnot necessary for gases exhausted from a furnace and a workingenvironment is good.

The nickel formate and the nickel acetate, among the nickel compounds ofcarboxylic acid, have a high solubility in water, and therefore can beapplied as an aqueous solution.

When the thickness of the mixture layer in which the metal nickel, thenickel oxide and the carbon atoms exist in a mixed state is too thick,resistance loss becomes large, whereas, when the thickness is too thin,the base protection becomes insufficient. The thickness of the mixturelayer is, accordingly, preferably from 0.001 μm to 1 μm.

The negative electrode for aqueous solution electrolysis of the presentinvention is one in which an electrode catalyst layer is formed on themixture layer surface of the electrode base. The electrode catalystlayer is formed of a layer including a platinum group metal or platinumgroup metal compound, and preferably a layer including the platinumgroup metal or platinum group metal compound, and a lanthanoid compound.

The components forming the electrode catalyst layer, i.e., the platinumgroup component including the platinum group metal or platinum groupmetal compound, and the lanthanoid component including the lanthanoidcompound, have a low hydrogen overvoltage and a high resistance as anegative electrode used in an ion-exchange membrane electrolysis of abrine.

In the negative electrode for aqueous solution electrolysis of thepresent invention, owing to the mixture layer of the electrode base, theelution of the nickel from the nickel substrate can be prevented, thepotential stability can be improved upon the start-up of the passage ofelectric current through the electrolytic cell, and the deterioration ofthe electrode caused by a reverse current can be effectively preventedwhen the electrolytic cell operation is suddenly shutdown. In addition,in the present invention, the deterioration of the electrolytic cell canbe effectively prevented during storage thereof before an electriccurrent is passed through the electrolytic cell.

The negative electrode for aqueous solution electrolysis in which theelectrode catalyst layer including the platinum group metal or platinumgroup metal compound, and the lanthanoid compound is formed furthermoreshows the properties.

The negative electrode for aqueous solution electrolysis of the presentinvention can be produced by, for example, a method described below.

First, the electrode base was produced in the same manner as describedabove. Then, the electrode catalyst layer is formed on the mixture layersurface of the electrode base.

The electrode catalyst layer can be formed by application of anelectrode catalyst-forming solution in which the platinum group metal orplatinum group metal compound, and optionally the lanthanoid compoundare dissolved or dispersed, and then thermal decomposition in anatmosphere containing oxygen.

The elements of the platinum group may include platinum, palladium,ruthenium, iridium, and the like. When the platinum is used, it ispreferable to dissolve it in the electrode catalyst layer-formingsolution as a dinitrodiammine platinum salt, and when the ruthenium isused, it is preferable to dissolved it in the electrode catalystlayer-forming solution as a ruthenium nitrate. In this way, the use of acompound including no chlorine enables prevention of a negativeinfluence on the mixture layer and the conductive substrate upon theformation of the electrode catalyst layer.

The lanthanoid elements may include lanthanum, cerium, praseodymium,neodymium, promethium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium and lutetium having anatomic number of 57 to 71, and the like. In particular, the lanthanumand cerium are preferably used. When the lanthanum is used as thelanthanoid element, calboxylic acid salts thereof such as lanthanumacetate are preferably used, and when the cerium is used, cerium nitrateis preferably used.

When the electrode catalyst layer includes both the platinum componentand the lanthanoid component, the atomic ratio of the platinum groupatoms to the lanthanoid atoms is preferably from 30/70 to 90/10 in theelectrode catalyst layer-forming solution.

The electrode catalyst layer is formed by applying the electrodecatalyst layer-forming solution to the mixture layer surface of theelectrode base, and drying and baking (thermal decomposition) it. Thethickness may be controlled by repeating the procedure of applying,drying and baking several times. The electrode catalyst layer-formingsolution applied is dried at 60 to 80° C. for 10 to 20 minutes, and itis baked at a temperature of 400 to 600° C. for 10 to 20 minutes in anatmosphere containing oxygen.

The thickness of the electrode catalyst layer formed is preferably from3 to 6 μm.

The thus formed electrode catalyst layer has a high catalytic activityin a hydrogen generation reaction as a negative electrode for aqueoussolution electrolysis, and can maintain a hydrogen overvoltage low for along time when electrolysis is performed at not only a low currentdensity but also a high current density. In addition, the negativeelectrode surface has a good current uniformity, and the ion-exchangemembrane can be prevented from the contamination with the heavy metals,even if the electrolysis is performed with the ion-exchange membranebeing in contact with the negative electrode.

In the negative electrode for aqueous solution electrolysis having thiselectrode catalyst layer, the electrode catalyst layer can be preventedfrom the deterioration due to oxidation and the like, even if thenegative electrode is exposed to the atmosphere.

The electrode catalyst layer formed by applying the electrode catalystlayer-forming solution to the electrode base, and then performing thethermal decomposition in the atmosphere containing oxygen does notinclude chlorine compounds as a component other than the metals formingthe metal compound which forms the electrode catalyst layer, andtherefore, it can be thought that any negative influence is not exertedon the conductive base, the mixture layer and the electrode catalystlayer.

Conventionally, when ruthenium oxide, which serves as the electrodecatalyst, is formed by heat in an atmosphere containing oxygen,ruthenium chloride is generally used, and therefore the electrodecatalyst layer formed has a chlorine compound. It is preferable to usesalts from which chlorine compounds are not generated such as rutheniumnitrate as in the present invention.

In the present invention, when the lanthanoid carboxylate is usedtogether with the ruthenium component, it is preferable to use at leastone lanthanum carboxylate selected from the group consisting of, forexample, lanthanum acetate, lanthanum formate and lanthanum oxalate, andmore preferably lanthanum acetate having a high solubility.

In particular, it can be thought that an oxycarbonate or carbonate maybe generated from the lanthanum carboxylate in the thermal decompositionstep forming the electrode catalyst layer in an atmosphere containingoxygen having a temperature of 400 to 600° C.

As a result, it is confirmed that the carbon atoms uniformly exist inthe electrode catalyst layer formed. In addition, it can be thought thatthe presence of the compound having carbon atoms in the electrodecatalyst layer due to the thermal decomposition of the lanthanumcarboxylate, also contributes to the electrochemical properties of thenegative electrode for aqueous solution electrolysis.

The electrode properties of the negative electrode for aqueous solutionelectrolysis of the present invention are not deteriorated even if theelectrolytic cell operation is shutdown, the electrode is taken out fromthe electrolytic cell, exposed to the atmosphere, and put in theelectrolytic cell again, and then the operation is resumed. This mayshow that the properties of the electrode catalyst layer formed from theruthenium nitrate and the lanthanum carboxylate are not changed in theatmosphere, and the conductive substrate of the electrode is coveredwith the dense mixture layer and electrode catalyst layer.

The deterioration due to the elution of the metal component from theconductive substrate is not caused, because the conductive substrate ofthe electrode is covered with the dense mixture layer and electrodecatalyst layer. As a result, an advantage can be obtained in which it isnot necessary to prevent the negative influence on the ion-exchangemembrane caused by the elution of the metal component and the stableoperation can be performed for a long term.

To the electrode catalyst layer-forming solution, which is used forforming the electrode catalyst layer, may be added a component includinga platinum compound having no chlorine atom in addition to the rutheniumcompound and the lanthanum carboxylate, whereby the platinum may becontained in the electrode catalyst layer.

The reason why some properties can be obtained by containing theplatinum in the electrode catalyst layer in addition to the rutheniumand lanthanum is not made clear, but the electrode catalyst layer isprevented from the performance deterioration after the passage ofelectric current, and an effect of inhibiting abrasion of the electrodecatalyst layer can be obtained.

When the platinum compound having no chlorine atom is added, the atomicratio of Pt/La in the electrode catalyst layer-forming solution ispreferably 0.005 or more. When the ratio is less than 0.005, sufficienteffects cannot be obtained.

As the platinum compound having no chlorine atom, at least one ofdinitrodiammine platinum and hexahydroxoplatinum acid may be used. Asufficient catalytic activity can be maintained in a hydrogen generationreaction for a long term, even if the thickness of the electrodecatalyst layer is 5 μm or less, because the abrasion of the electrodecatalyst layer can be more effectively inhibited due to the presence ofthe platinum.

The electrode catalyst layer is formed by heat-treatment in theatmosphere containing oxygen at a temperature of preferably 400° C. to600° C., and more preferably 460° C. to 540° C. When the temperature islower than 400° C., it is hard to form a coating layer having a highelectrode catalytic activity in the hydrogen generation reaction;whereas when it is higher than 600° C., the conductive substrate becomeseasily oxidized. The atmosphere containing oxygen may include the air,an atmosphere containing 100% by volume of oxygen, and the like.

It can be thought that when the electrode catalyst layer includes theplatinum, the corrosion of the nickel base may be easily caused due togalvanic corrosion, because the platinum have a more nobleoxidation-reduction potential. According to the electrode base of thepresent invention, however, the corrosion reaction of the electrode basecan be inhibited, because it has the mixture layer including the metalnickel, nickel oxide and carbon atoms on the conductive substratesurface, and therefore it is also possible to inhibit the corrosion ofnickel in the electrode base in the case where the electrode baseincludes the electrode catalyst layer including the platinum.

When the noble metal is used in the electrode catalyst layer of thenegative electrode for aqueous solution electrolysis, it is feared thatthe elution of the nickel of the base, caused during the storage beforethe passage of electric current or during the suspension of the passageof electric current, damages the ion-exchange membrane. This phenomenonis more markedly shown in a condition in which the negative electrode isstored after the electrolysis is performed or the passage of electriccurrent is stopped than a condition in which the negative electrode foraqueous solution electrolysis is not used in the electrolysis yet.

This may be because the nickel surface of the base is likely to giverise to the corrosion reaction after the electrolysis, though the nickelsurface of the base is covered with the stable oxide layer before theelectrolysis operation.

Examples and Comparative Examples described below show comparisons of anickel contamination into an ion-exchange membrane when a negativeelectrode for aqueous solution electrolysis was brought into contactwith an ion-exchange membrane after the start of the passage of electriccurrent. The elusion of nickel was not observed from the unelectrolyzedsample in the mixture layer formed from the nickel carboxylate; whereasthe elusion of nickel was observed in a case where nickel sulfate wasused as a coating material for forming the mixture layer, despite thesample was not subjected to the electrolysis. The component analysis ofthis mixture layer shows that the nickel sulfate is not thermallydecomposed and remains in a salt form, and therefore it can beunderstood that the stable mixture layer is not formed.

The nickel oxide is more easily formed when baking at a hightemperature, but the initial potential stability at the start ofelectrolysis can be more improved when the mixture layer is formed at alower temperature.

As shown in Examples and Comparative Examples described below, themixture layer including the metal nickel, the nickel oxide and thecarbon atoms is characterized by a higher corrosion resistance than thenickel oxide layer formed by baking the nickel base in the atmospherewhen anodic polarization occurs, and characterized that the destructionof the mixture layer is not advanced even when the anodic polarizationoccurs.

Consequently, the destruction of the mixture layer is not advanced evenwhen the negative electrode is anodically polarized to flow the reversecurrent, which occurs, for example, at emergency stop of electrolysisduring the electrolytic cell operation, and the same performance as thatbefore the operation is shutdown can be shown after the electric currentis passed again.

This shows that in the present invention the nickel carboxylate, whichcan be formed at a low temperature, is preferably used for the mixturelayer formed on the surface of the electrode base, in the negativeelectrode for aqueous solution electrolysis having the electrodecatalyst layer including the platinum group metal or the compoundthereof.

It is also shown that the mixture layer formed by the thermaldecomposition of nickel carboxylate is preferable, in a case where themixture layer is formed in low-temperature baking conditions forimproving the potential stability after the start of the passage ofelectric current through the electrolytic cell.

EXAMPLES

The present invention will be explained below, showing Examples andComparative Examples.

Example 1 Anodic Polarization Test of Electrode Base

A surface of a nickel expanded metal having a thickness of 0.9 mm, alength of 20 mm and a width of 20 mm was sand-blasted with aluminaparticles having a particle size of 50 μm to roughen the surface,thereby obtaining a conductive substrate for a sample.

The conductive substrate was immersed in 30% by mass sulfuric acidhaving a temperature of 60° C. for 10 minutes to perform etching,thereby removing the surface oxide coating film and the remainingalumina particles.

Next, an aqueous solution including 0.1 mol/L nickel formate (II)dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) wasprepared to be used as a coating solution for a mixture layer. Thecoating solution for a mixture layer was applied to the nickel expandedmetal which had been surface-treated, and the resulting metal was driedat 60° C. for 3 minutes and baked in a muffle furnace (KDF-P80Gmanufactured by Denken Co., Ltd.) at 300° C. for 10 minutes to give asample 1 (electrode base) for an anodic polarization test. Using thesample 1 as a negative electrode and a 20 mm×20 mm nickel expanded metalas a positive electrode, a first pre-electrolysis was performed at acurrent density of 10 kA/m² for one hour using an aqueous 32% by masssodium hydroxide solution having a temperature of 90° C. as anelectrolytic solution.

After the pre-electrolysis was stopped, a first anodic polarization testwas performed in which the direction of the passage of electric currentwas immediately reversed, the anodic polarization test sample 1 wassubjected to anodic polarization at a current density of 10 A/m², achange in the electrode potential of the anodic polarization test sample1 to a mercury/mercury oxide reference electrode in an electric quantitywas determined until the electrode potential was suddenly increased fromthe oxidation-reduction potential of the nickel to a noble potential,and the passage of electric current was intercepted. The results areshown in FIG. 1 as Test 1.

Subsequently, the direction of the passage of electric current wasreversed, and a second pre-electrolysis was performed in the same manneras in the first electrolysis. After that, a second anodic polarizationtest was performed. The results are shown in FIG. 1 as Anodicpolarization test 2.

Furthermore, a third pre-electrolysis and anodic polarization wasperformed in the same manner as above, and the results are shown in FIG.1 as Anodic polarization test 3.

Comparative Example 1 Comparative Anodic Polarization Test of OxideLayer

Instead of the anodic polarization test sample 1 in Example 1, acomparative anodic polarization test sample 1 was made by baking aconductive substrate at 500° C. for 10 minutes to form a nickel oxidecoating film. A first comparative anodic polarization test, a secondcomparative anodic polarization test and a third comparative anodicpolarization test were performed in the same manner as in Example 10.

The results are shown in FIG. 1 as Comparative anodic polarization test1, Comparative anodic polarization test 2 and Comparative anodicpolarization test 3.

The results show that the electrode base of the present invention has ahigher resistance to an electric current generated by the anodicpolarization and oxidizing the negative electrode than that of the oxidecoating film formed by the oxidation of the substrate nickel formed inthe atmosphere.

Example 2 Confirmation of Thermal Decomposition Products of NickelFormate

The aqueous nickel formate solution prepared in Example 1 was applied toa nickel plate and a procedure of baking at 300° C. in the atmospherewas repeated ten times to produce a sample 1 for confirmation of thermaldecomposition products.

Ten portions on the surface coated with nickel formate and baked of thesample 1 for confirmation of thermal decomposition products weremeasured using an energy dispersive X-ray analyzer (Genesis-XM 2manufactured by EDAX Inc.).

The abundance ratio of nickel, oxygen and carbon was 45.5:39.8:14.7 byatom on an average of the ten portions.

After that, a sample 2 for confirmation of thermal decompositionproducts was produced in the same manner as above except that the bakingtemperature was changed to 500° C., and the measurement was performed inthe same manner as above. The abundance ratio of nickel, oxygen andcarbon was 51.4:36.7:11.9 by atom on an average of the ten portions.

The presence of carbon could be confirmed on all of the samples.

Comparative Example 2

A comparative sample 1 for confirmation of thermal decompositionproducts was produced by repeating the procedure of baking at 300° C. inthe atmosphere ten times in the same manner as in Example 2, except thatthe aqueous nickel formate solution was not applied to the nickel plate.The products on the surface were measured in the same manner as inExample 2. The abundance ratio of nickel, oxygen and carbon was91.1:8.9:0 by atom.

After that, a comparative sample 2 for confirmation of thermaldecomposition products was produced in the same manner as above exceptthat the baking temperature was changed to 500° C., and the samemeasurement as above was performed. The abundance ratio of nickel,oxygen and carbon was 80.9:19.1:0 by atom on an average of ten portions.

It was found that there was no carbon on all of the comparative samplesfor confirmation of thermal decomposition products.

Examples 3 and 4, and Comparative Example 3

Each of samples of nickel acetate, nickel formate and nickel nitratewhich were heated at 300° C. and 500° C. in the atmosphere for 10minutes was measured using an X-ray diffractometer (X'Pert PRO MPDmanufactured by PANalytical, target: copper, accelerating voltage: 45kV). The measurement results are shown in Table 1 as an atomic ratio ofnickel oxide (NiO) or nickel metal (Ni).

TABLE 1 Thermal decomposition Nickel temperature Nio Ni Undecomposedcompound (° C.) (%) (%) salt (%) Example 3 Nickel 300 65 35 0 acetateNickel 500 83 17 0 acetate Example 4 Nickel 300 69 31 0 formate Nickel500 96 4 0 formate Comparative Nickel 300 84 0 16 example 3 nitrateNickel 500 100 0 0 nitrate

Example 5

The nickel formate powder used in Example 1 was heated at 300° C. and500° C. in the atmosphere to perform thermal decomposition. Theresulting sample was measured for an X-ray absorption fine structure(XAFS) using beam line BL-12C in Radiation Science Research Facility(Photon Factory) of High Energy Acceleration Research Organization.

The measurement was performed under conditions described below.Spectrometer: an Si (111) two crystal spectrometer. Mirror: a focusingmirror. Absorption edge: a transmission method.

Detector used: Ionization chamber. The abundance ratio was obtainedusing XANES spectra.

The measured results were obtained according to a general analysismethod of XANES spectra in which a computation process was performed sothat a difference between a synthesized peak which was synthesized fromthe standard peaks of the metal nickel and the nickel oxide which couldbe thought as the components based on the measured peak, and a measuredpeak becomes the minimum in a least squares method. The percentage wasshown as the abundance ratio of each component.

The nickel formate which had been thermally decomposed at 300° C. had31.6% of metal nickel and 68.4% of nickel oxide.

The nickel formate which had been thermally decomposed at 500° C. had18.6% of metal nickel and 81.4% of nickel oxide.

Example 6

A surface of a nickel expanded metal having a thickness of 0.9 mm, alength of 20 mm and a width of 20 mm was sand-blasted with aluminaparticles having a particle size of 50 μm to roughen the surface,thereby obtaining a conductive substrate for a sample.

The conductive substrate was immersed in 30% by mass sulfuric acidhaving a temperature of 60° C. for 10 minutes to perform etching,thereby removing the surface oxide coating film and the remainingalumina particles.

Next, an aqueous solution including 0.1 mol/L nickel acetate (II)tetrahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) wasprepared to be used as a coating solution for a mixture layer. Thecoating solution for a mixture layer was applied to the nickel expandedmetal which had been surface-treated, and the resulting metal was driedat 60° C. for 3 minutes and baked in a muffle furnace (KDF-P80Gmanufactured by Denken Co., Ltd.) at 300° C. for 10 minutes to give asample 1-1 (electrode base) on which the mixture layer was formed, orbaked at 500° C. for 10 minutes to give a sample 1-2 (electrode base) onwhich the mixture layer was formed.

After that, an electrode catalyst layer-forming solution 1 which was asolution of ruthenium nitrate-lanthanum acetate-dinitrodiammine platinumnitrate in an atomic ratio of Ru:La:Pt=1:1:0.05 using a solution ofruthenium nitrate in nitric acid (manufactured by Tanaka Kikinzoku KogyoCo., Ltd.), a lanthanum acetate n-hydrate (manufactured by Wako PureChemical Industries, Ltd.) and a dinitrodiammine platinum nitratesolution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.).

The electrode catalyst layer-forming solution 1 was coated to themixture layer-formed sample 1-1 or 1-2 previously produced and wasdried, and a procedure of baking at 500° C. for 10 minutes was repeatedfive times to produce test negative electrodes 1-1 and 1-2.

Electrolysis was performed in an aqueous solution including 30% by massof sodium hydroxide at 90° C. at a current density of 10 kA/m² for onehour using the test negative electrode 1-1 or 1-2 produced and the samenickel expanded metal as that used in the base of the test negativeelectrode 1-1 as a positive electrode, and electrolysis was continued ata current density of 20 kA/m² for further one hour.

The surfaces of the test negative electrodes 1-1 and 1-2 were observedafter the electrolysis by using a scanning electron microscope (JSM-6490manufactured by JEOL Ltd.) about peeling-off of the coating film, andthe like. The results are shown in Table 2.

Elution Test of Nickel after Electrolysis

The test negative electrode 1-1 or 1-2 after the electrolysis wasbrought into close contact with a positive ion-exchange membrane (N-2030manufactured by Du Pont), which had been immersed in an aqueous sodiumhydroxide solution having a pH of 11, and a pressure of 981 Pa wasapplied thereto, which was sealed in a polyethylene bag and allowed tostand for 24 hours.

After that, nickel in the positive ion-exchange membrane taken out wasdetected using an ICP emission spectrophotometric analyzer (ICPS-8100manufactured by Shimadzu Corporation). The results are shown in Table 2as a nickel deposition amount per 4 cm² area.

Example 7

A test negative electrode 2-1 whose mixture layer was formed at 300° C.and a test negative electrode 2-2 whose mixture layer was formed at 500°C. were produced in the same manner as in Example 6, except that nickelformate was used as the mixture layer-forming material instead of thenickel acetate, and the evaluation test was performed in the same manneras in Example 6. The results are shown in Table 2.

Example 8

A mixture layer-formed sample 3-1 whose mixture layer was formed at 300°C. and a mixture layer-formed sample 3-2 whose mixture layer was formedat 500° C. were produced in the same manner as in Example 6.

Then, cerium nitrate and a dinitrodiammine platinum salt were dissolvedin 8% by mass nitric acid so that the atomic ratio of Pt:Ce was 1:1 toprepare an electrode catalyst layer-forming solution 2 having a totalconcentration of cerium and platinum of 5% by mass.

The electrode catalyst layer-forming solution 2 was applied and dried,and a procedure of baking at 500° C. for 10 minutes was repeated fivetimes to produce test negative electrodes 3-1 and 3-2. The evaluationtest was performed in the same manner as in Example 6. The results areshown in Table 2.

Example 9

A mixture layer-formed sample 4-1 whose mixture layer was formed at 300°C. and a mixture layer-formed sample 4-2 whose mixture layer was formedat 500° C. were produced in the same manner as in Example 7.

Next, the electrode catalyst layer-forming solution 2 was applied to thesample and dried, and a procedure of baking at 500° C. for 10 minuteswas repeated five times in the same manner as in Example 8 to producetest negative electrodes 4-1 and 4-2. The evaluation test was performedin the same manner as in Example 6. The results are shown in Table 2.

Comparative Example 4

A comparative negative electrode 2-1 whose mixture layer was formed at300° C. and a comparative negative electrode 2-2 whose mixture layer wasformed at 500° C. were produced in the same manner as in Example 6,except that nickel sulfate was used for the mixture layer instead ofnickel acetate. The evaluation test was performed in the same manner asin Example 6. The results are shown in Table 2.

Comparative Example 5

A comparative negative electrode 2-1 whose mixture layer was formed at300° C. and a comparative negative electrode 2-2 whose mixture layer wasformed at 500° C. were produced in the same manner as in Example 6,except that nickel nitrate was used for the mixture layer instead of thenickel acetate. The evaluation test was performed in the same manner asin Example 6. The results are shown in Table 2.

Comparative Example 6

A comparative negative electrode 3 was produced in the same manner as inExample 6, except that the mixture layer was not formed. The evaluationtest was performed in the same manner as in Example 6. The results areshown in Table 2.

Comparative Example 7

A comparative negative electrode 4 was produced in the same manner as inExample 6, except that a mixture layer was formed by baking theconductive substrate at 500° C. in the atmosphere without applying anickel salt such as nickel acetate. The evaluation test was performed inthe same manner as in Example 6. The results are shown in Table 2.

Comparative Example 8

A comparative negative electrode 5-1 whose mixture layer was formed at300° C. and a comparative negative electrode 5-2 whose mixture layer wasformed at 500° C. were produced in the same manner as in Example 8,except that nickel sulfate was used for the mixture layer instead of thenickel acetate. The evaluation test was performed in the same manner asin Example 6. The results are shown in Table 2.

Comparative Example 9

A comparative negative electrode 6-1 whose mixture layer was formed at300° C. and a comparative negative electrode 6-2 whose mixture layer wasformed at 500° C. were produced in the same manner as in Example 8,except that nickel nitrate was used for the mixture layer instead of thenickel acetate. The evaluation test was performed in the same manner asin Example 6. The results are shown in Table 2.

Comparative Example 10

A comparative negative electrode 7 was produced in the same manner as inExample 8, except that the mixture layer was not formed. The evaluationtest was performed in the same manner as in Example 6. The results areshown in Table 2.

Comparative Example 11

A comparative negative electrode 8 was produced in the same manner as inExample 8, except that a mixture layer was formed by baking theconductive substrate at 500° C. in the atmosphere without applying anickel salt such as nickel acetate. The evaluation test was performed inthe same manner as in Example 6. The results are shown in Table 2.

TABLE 2 Presence or Elements absence Intermediate layer Ni contained ofConcentration deposition in surface Coating of coating Baking amountelectrode peeling- solution solution temperature (μg/4 cm²) catalyst offExample 6 Test negative Nickel 0.1 mol/L 300° C. 4.7 Ru La Pt Absenceelectrode 1-1 acetate Test negative Nickel 0.1 mol/L 500° C. 4.0 Ru LaPt Absence electrode 1-2 acetate Example 7 Test negative Nickel 0.1mol/L 300° C. 7.5 Ru La Pt Absence electrode 2-1 formate Test negativeNickel 0.1 mol/L 500° C. 7.0 Ru La Pt Absence electrode 2-2 formateExample 8 Test negative Nickel 0.1 mol/L 300° C. 9.0 Ce Pt Absenceelectrode 3-1 acetate Test negative Nickel 0.1 mol/L 500° C. 7.0 Ce PtAbsence electrode 3-2 acetate Example 9 Test negative Nickel 0.1 mol/L300° C. 8.0 Ce Pt Absence electrode 4-1 formate Test negative Nickel 0.1mol/L 500° C. 9.0 Ce Pt Absence electrode 4-2 formate ComparativeComparative Nickel 0.1 mol/L 300° C. 14.3 Ru La Pt Absence example 4test negative sulfate electrode 1-1 Comparative Nickel 0.1 mol/L 500° C.10.0 Ru La Pt Absence test negative sulfate electrode 1-2 ComparativeComparative Nickel 0.1 mol/L 300° C. 29.0 Ru La Pt Absence example 5test negative nitrate electrode 2-1 Comparative Nickel 0.1 mol/L 500° C.6.0 Ru La Pt Absence test negative nitrate electrode 2-2 ComparativeComparative No formation 15.3 Ru La Pt Absence example 6 test negativeelectrode 3 Comparative Comparative Oxidation in the 500° C. 4.0 Ru LaPt Absence example 7 test negative atmosphere electrode 4 ComparativeComparative Nickel 0.1 mol/L 300° C. 23.0 Ce Pt Absence example 8 testnegative sulfate electrode 5-1 Comparative Nickel 0.1 mol/L 500° C. 18.0Ce Pt Absence test negative sulfate electrode 5-2 ComparativeComparative Nickel 0.1 mol/L 300° C. 19.0 Ce Pt Absence example 9 testnegative nitrate electrode 6-1 Comparative Nickel 0.1 mol/L 500° C. 13.0Ce Pt Absence test negative nitrate electrode 6-2 ComparativeComparative No formation 18.0 Ce Pt Absence example 10 test negativeelectrode 7 Comparative Comparative Oxidation in the 500° C. 9.0 Ce PtAbsence example 11 test negative atmosphere electrode 8

Example 10

A mixture layer was formed at 300° C. in the same manner as in Example 6except that a nickel expanded metal having a thickness of 0.15 mm wasused as the conductive substrate. The same electrode catalystlayer-forming solution 1 as in Example 6 was applied thereto, and a testnegative electrode 5 was produced in the same manner as in Example 6.

Evaluation of Electrode Performance

On a test electrolytic cell were mounted the test negative electrode 5produced above as the negative electrode and an electrode for generatingchlorine whose base was a titanium expanded metal (DSE JP-202manufactured by Permelec Electrode Ltd.) as a positive electrode, and anegative electrode room and a positive electrode room were divided witha positive ion-exchange membrane (N-2030 manufactured by Du Pont)treated with an aqueous solution of 2% by mass sodium hydroxide. Azero-gap ion-exchange membrane in which the negative electrode, theion-exchange membrane and the positive electrode were integrally touchedwas assembled. The electrolytic cell was stored for 15 hours after theassembly without filling an electrolytic solution therein.

Then, while a brine having a concentration of 200 g/L as an anolyte andan aqueous sodium hydroxide solution having a concentration of 32% bymass as a catholyte were circulated, electrolysis was performed at anoperation temperature of 90° C. at a current density of 6 kA/m².

In a 100-day electrolysis term, electrolysis was stopped for two days ofthe 51st day and 52nd day, and the electrolytic cell was disassembledand stored under exposure to the atmosphere. After the storage, theelectrolysis was performed, but the increase of the electrolytic cellvoltage was not observed and the current efficiency was kept at 97%.

After the 100-day electrolysis, the electrolytic cell was disassembled,and the ion-exchange membrane was observed. The deposition of nickel wasnot found.

Evaluation of Short-Circuit Performance

Only ion-exchange membrane was exchanged in the test electrolytic cellwhich was disassembled for the evaluation of electrode performance, andthe electrolysis was performed again. After it was confirmed that theflowing current was stabled at a current density of 6 kA/m², anelectrolysis current was stopped, and supply and discharge of theanolyte and the catholyte was stopped in a state in which the positiveelectrode and the negative electrode were short circuited, and theelectrolytic cell was allowed to stand at 70° C. for 2 hours.

After that, the electrolysis operation was re-started at a currentdensity of 6 kA/m², and a test for determining degradation ofperformances after 10 days was repeated twice.

After the first short-circuit test, the electrolytic cell voltage wasincreased by 0.004 V and the hydrogen overvoltage was increased by 0.7mV.

After the second short-circuit test, the electrolytic cell voltage wasincreased by 0.004 V and the hydrogen overvoltage was increased by 2.4mV. That is to say, the increase of the electrolytic cell voltage wasonly 0.008 V and the increase of the hydrogen overvoltage was only 3.1mV after the second short-circuit test, compared to those before thefirst short-circuit test.

Comparative Example 12

A comparative test negative electrode 9 was produced in the same manneras in Example 10, except that a mixture layer was formed by baking aconductive substrate at 500° C. for 10 minutes instead of formation of amixture layer by the application of the nickel salt and the thermaldecomposition, and the electrolysis was performed in the same manner asin Example 10. The initial electrolytic cell voltage showed a voltage0.010 V higher than that in Example 10. In a 100-day electrolysis term,electrolysis was stopped for two days of the 51st day and 52nd day, andthe electrolytic cell was disassembled and stored under exposure to theatmosphere, in the same manner as in Example 10. The increase of theelectrolytic cell voltage was not observed in the subsequentelectrolysis, and the current efficiency was kept at 97%. However, theelectrolytic cell voltage was increased by 0.010 V. In addition, thenickel deposition to the ion-exchange membrane was not confirmed afterthe electrolytic cell was disassembled.

The short-circuit test was performed twice in the same manner as inExample 10.

After the first short-circuit test, the electrolytic cell voltage wasincreased by 0.007 V, and the hydrogen overvoltage was increased by 7.0mV.

After the second short-circuit test, the electrolytic cell voltage wasincreased by 0.018 V, and the hydrogen overvoltage was increased by 6.2mV. That is to say, the electrolytic cell voltage was increased by 0.025V and the hydrogen overvoltage was increased by 13.2 mV after the secondshort-circuit test, compared to those before the first short-circuittest.

The present application claims benefit of priority of Japanese PatentApplication No. 2010-032578 filed on Feb. 17, 2010, the contents ofwhich are hereby incorporated by reference.

INDUSTRIAL APPLICABILITY

The negative electrode for aqueous solution electrolysis of the presentinvention has a low hydrogen overvoltage; nickel on the conductivesubstrate surface does not elute even when the passage of electriccurrent is stopped; only a small amount of nickel is deposited in theion-exchange membrane when it is used as a negative electrode in theion-exchange membrane electrolytic cell; the operation can be stablyperformed for a long term; the electrolysis voltage is kept stable fromthe beginning of the electrolysis even when the platinum electrodecatalyst layer is formed; and it is possible to stably operate theelectrolytic cell. The negative electrode for aqueous solutionelectrolysis of the invention having the effects described above ispreferably used for the electrolysis of an aqueous solution of an alkalimetal halide, and the like.

1. An electrode base for forming an electrode catalyst layer comprisinga mixture layer including metal nickel, a nickel oxide and carbon atomsformed on a surface of a conductive substrate having a nickel surface.2. The electrode base according to claim 1, wherein the mixture layer isformed by applying a nickel compound including a nickel atom, a carbonatom, an oxygen atom and a hydrogen atom to the surface of theconductive substrate, and performing a thermal decomposition.
 3. Theelectrode base according to claim 2, wherein the nickel compound iseither of a nickel formate and a nickel acetate.
 4. A negative electrodefor aqueous solution electrolysis comprising: a conductive substratehaving a nickel surface; a mixture layer including metal nickel, anickel oxide and carbon atoms, formed on the surface of the conductivesubstrate; and an electrode catalyst layer including a platinum groupmetal or a platinum group metal compound, formed on a surface of themixture layer.
 5. The negative electrode for aqueous solutionelectrolysis according to claim 4, wherein the electrode catalyst layerfurther includes a lanthanoid compound.
 6. The negative electrode foraqueous solution electrolysis according to claim 5, wherein theelectrode catalyst layer is formed by thermally decomposing an electrodecatalyst layer-forming solution including a ruthenium nitrate and alanthanum acetate at 400° C. to 600° C. in an atmosphere containingoxygen.
 7. The negative electrode for aqueous solution electrolysisaccording to claim 6, wherein the electrode catalyst layer-formingsolution further includes a platinum compound.
 8. The negative electrodefor aqueous solution electrolysis according to claim 5, wherein theelectrode catalyst layer includes a cerium oxide and platinum.
 9. Amethod for producing an electrode base for forming an electrode catalystlayer, the method comprising the steps of: applying a nickel compoundincluding a nickel atom, a carbon atom, an oxygen atom and a hydrogenatom to a surface of a conductive substrate having a nickel surface; andperforming thermal decomposition at 250° C. to 600° C. in an atmospherecontaining oxygen, thereby forming a mixture layer including metalnickel, a nickel oxide and carbon atoms.
 10. The method for producing anelectrode base according to claim 9, wherein the nickel compound iseither of a nickel formate and a nickel acetate.
 11. A method forproducing a negative electrode for aqueous solution electrolysiscomprising the steps of: producing an electrode base by applying anickel compound including a nickel atom, a carbon atom, an oxygen atomand a hydrogen atom to a surface of a conductive substrate having anickel surface, and performing thermal decomposition at 250° C. to 600°C. in an atmosphere containing oxygen, thereby forming a mixture layerincluding metal nickel, a nickel oxide and carbon atoms; and forming anelectrode catalyst layer by applying an electrode catalyst layer-formingsolution including a platinum group metal compound to a surface of themixture layer of the electrode base, and performing thermaldecomposition in an atmosphere containing oxygen.
 12. The method forproducing a negative electrode for aqueous solution electrolysisaccording to claim 11, wherein the nickel compound is either of a nickelformate or a nickel acetate.
 13. The method for producing a negativeelectrode for aqueous solution electrolysis according to claim 11,wherein the electrode catalyst layer-forming solution includes aruthenium nitrate and a lanthanum acetate, and the electrode catalystlayer is formed by applying this electrode catalyst layer-formingsolution to the surface of the mixture layer of the electrode base andthen performing thermal decomposition at 400° C. to 600° C. in anatmosphere containing oxygen.
 14. The method for producing a negativeelectrode for aqueous solution electrolysis according to claim 13,wherein the electrode catalyst-forming solution further includes aplatinum compound.
 15. The method for producing a negative electrode foraqueous solution electrolysis according to claim 11, wherein theelectrode catalyst layer-forming solution further includes a ceriumnitrate.